Nucleic acid hybridization assays are based on the tendency of two single-stranded nucleic acid sequences to pair at their complementary regions. Presently, nucleic acid hybridization assays are primarily used to detect and identify unique DNA or RNA base sequences or specific genes in a complete DNA molecule, in mixtures of nucleic acids, or in mixtures of nucleic acid fragments.
The identification of unique DNA or RNA sequences or specific genes within the total DNA or RNA extracted from tissue or culture samples may indicate the presence of physiological or pathological conditions. In particular, the identification of unique DNA or RNA sequences or specific genes within the total DNA or RNA extracted from human or animal tissue may indicate the presence of genetic diseases or conditions such as sickle cell anemia, cancer and precancerous states, or bacterial or viral infections.
On the other hand, the identification of unique DNA or RNA sequences or specific genes within the total DNA or RNA extracted from bacterial cultures may indicate the presence of antibiotic resistance, toxicants, viral or plasmid born conditions, or provide for identification of different types of bacteria.
Further potential for nucleic acid hybridization assays exists in agriculture and food processing where nucleic acid hybridization assays may be used to detect plant pathogenesis or toxicant producing bacteria.
Luminescent labels emit light upon excitation by an external energy source and may be grouped into categories dependent upon the source of the exciting energy, including: photoluminescent or fluorescent labels which are excitable by units of electromagnetic radiation of infrared, visible, or ultraviolet light; chemiluminescent labels which obtain energy from chemical reactions; radioluminescent labels excitable by energy from high energy particles; and bioluminescent labels for which the exciting energy is supplied in a biological system.
The use of luminescent labels allows for the development of "homogeneous" assay techniques in which the labeled probe employed exhibits different luminescent characteristics when associated with a target from those when unassociated, thereby obviating the need for separation of the associated and unassociated labeled probe. E.g., see Morrison et al. Anal. Biochem. 183:231 (1989).